1. Field of the Invention
The present invention generally relates to a power factor correction apparatus.
2. Description of Related Art
The apparent power generated by a three-phase generator is transmitted in transmission lines to various loads, such as an electric motor. In theory, the apparent power has been divided into two parts: one part is an active power actually being consumed by the loads, and the other part is a reactive power wasted in electromagnetic actions occurring in the transmission lines. In order to depict a relationship between these powers, a power factor is defined as a ratio of the active power to the apparent power.
In practice, in order to save the reactive power wasted in electromagnetic actions in the transmission lines, the active power needs to be increased, i.e., the power factor needs to be increased. Normally, a capacitor is connected in parallel with the electric motor to increase the power factor. There are two correction methods for correcting the power factor available in the market, including a static correction method and a dynamic correction method.
The static correction method includes the following steps of: predetermining a power factor according to the state of the transmission lines, choosing a capacitor corresponding to the power factor, connecting the capacitor to the transmission lines. However, the state of the transmission lines often varies, so the static correction method cannot accurately correct the power factor when the state is changed.
The dynamic correction method includes the following steps of: predetermining a power factor according to state of transmission lines, presetting a range of the power factor, choosing a plurality of capacitors according to the range of the power factor, connecting the capacitors to a microcomputer, determining when the capacitors is electrically connected to the transmission lines and how many capacitors are electrically connected to the transmission lines. Accordingly, the dynamic correction method can correct the power factor dynamically even if the state of the transmission lines changes.
Referring to FIG. 3, a three-phase generator 70 is connected to a load 80 via transmission lines 10. A conventional dynamic power factor correction apparatus 11 is used for correcting a power factor of the transmission lines 10. The dynamic power factor correction apparatus 11 includes a first sample circuit 20, a second sample circuit 30, a microcomputer 40, a switch 50, and a compensator 60. The first sample circuit 20 and the second sample circuit 30 are electrically connected to the transmission lines 10. The microcomputer 40 is electrically connected to the first sample circuit 20 and the second sample circuit 30. The switch 50 is electrically connected to the microcomputer 40, the compensator 60, and the transmission lines 10.
The first sample circuit 20 samples a voltage from the transmission lines 10. The second sample circuit 30 samples a current from the transmission lines 10. The microcomputer 40 receives the voltage and the current, and generates a control signal. The switch 50 receives the control signal, and is closed to electrically connect the compensator 50 to the transmission lines 10.
However, the microcomputer is expensive, making the power factor correction apparatus also expensive.
Therefore, a power factor correction apparatus is needed in the industry to address the aforementioned deficiencies and inadequacies.